Access new objects location after separation of mesh?
After you separate the meshes their origins are still the same as when they were together. This is normal behaviour. After you separate the meshes into its parts you need to set origin to geometry for every newly created mesh.

import bpy

for object in bpy.context.selected_objects:
    bpy.ops.object.origin_set(type='ORIGIN_GEOMETRY')  # set origin to geometry


After you do this you will be able to successfully query the new locations.